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Hydraulic Flow Circuits
Traction Circuit
The traction circuit piston pump is a variable displace-
ment pump that is directly coupled to the engine fly-
wheel. Pushing the top of the traction pedal rotates the
pump swash plate to create a flow of oil for forward ma-
chine movement. Pushing the bottom of the traction
pedal rotates the pump swash plate to cause oil flow for
reverse machine movement. This oil is directed to the
rear wheel motors. Operating pressure on the high pres-
sure side of the closed traction circuit loop is determined
by the amount of load developed at the fixed displace-
ment wheel motors. As the load increases, circuit pres-
sure can increase to relief valve settings: 4000 PSI in
either forward or reverse. If pressure exceeds the relief
setting, oil flows through the relief valve to the low pres-
sure side of the closed loop circuit.
Traction circuit pressure (forward or reverse) can be
measured by installing a tee fitting and gauge into the
traction system hydraulic lines.
The piston (traction) pump and wheel motors use a
small amount of hydraulic oil for internal lubrication. Oil
is designed to leak across pump and motor parts into the
case drain. This leakage results in the loss of hydraulic
oil from the closed loop traction circuit that must be re-
placed.
The piston (traction) pump incorporates a charge pump
that provides make–up oil for the traction circuit. This
gerotor gear pump is driven by the piston pump drive
shaft. It provides a constant supply of charge oil to the
traction circuit to make up for oil that is lost due to inter-
nal leakage in the piston pump and wheel motors.
Charge pump flow is directed through the oil filter and to
the low pressure side of the closed loop traction circuit.
Pressure in the charge circuit is limited by a relief valve
located in the charge plate adapter on the rear of the pis-
ton pump. Charge pump pressure can be measured at
the auxiliary test port on the side of the piston pump.
Hydraulic
System
Multi Pro 5700–D Page 4 – 9 Hydraulic System